The present invention relates to color measurement engines, and more particularly to engines providing UV filtering of the illumination.
Color measurement engines are well known and widely used in a variety of color measurement instruments. Typically, the engine includes a source of illumination for illuminating a sample, one or more detectors for detecting light reflected from (or transmitted through) the sample, and one or more filters for filtering the reflected (or transmitted) light. The detectors measure the light at various frequencies within the visible spectrum and provide an output indicative of the measured light.
It is sometimes desirable to provide ultraviolet (UV) filtering of the illumination, because a UV illumination component can cause the sample to emit or fluoresce visible light. On different occasions, readings including UV illumination and excluding UV illumination are desired. Additionally, useful information can be derived by comparing the UV-included and UV-excluded measurements. To provide selectable UV filtering, prior artisans have included a removable UV filter. When filtering is desired, the filter is installed over the illuminator, for example, by snap fitting the filter onto the instrument. When filtering is not desired, the filter is removed.
UV illumination filters suffer several disadvantages. First, the optical path between the illuminator and the sample is different when a filter is included than when the filter is removed. This difference results in inconsistent illumination patterns on the sample. Second, the filter must be carefully stored when removed from the instrument. Unfortunately, users do not always exercise care when doing so, and consequently the filters can become damaged, soiled, and/or lost. Third, when the filters are removed, dirt and other contaminants can enter the engine.